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• Oxford University Press  (12)
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• 1
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Oxford University Press
Publication Date: 2015-11-06
Description: Recent timing observation reported that the radio pulsar PSR J1734–3333 with a rotating period P = 1.17 s is slowing down with a period derivative $\dot{P}=2.28\times 10^{-12}\ \rm s\,s^{-1}$ . Its derived braking index n  = 0.9 ± 0.2 is the lowest value among young radio pulsars with the measured braking indices. In this Letter, we attempt to investigate the influence of the braking torque caused by the interaction between the fall-back disc and the strong magnetic field of the pulsar on the spin evolution of PSR J1734–3333. Analytical result show that this braking torque is obviously far more than that by magnetic dipole radiation for pulsars with spin period of 〉0.1 s, and play an important role during the spin-down of the pulsars. Our simulated results indicate that, for some typical neutron star parameters, the braking index and the period derivative approximately in agreement with the measured value of PSR J1734–3333 if the material inflow rate in the fall-back disc is 2 x 10 17 g s – 1 . In addition, our scenario can account for the measured braking indices of four young pulsars. However, our predicted X-ray luminosity are one to two order of magnitude higher than the observation. We proposed that this discrepancy may originate from the instability of fall-back disc.
Print ISSN: 1745-3925
Electronic ISSN: 1745-3933
Topics: Physics
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• 2
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Oxford University Press
Publication Date: 2015-12-13
Description: Because of the lack of long-term pulsed emission in quiescence and the strong timing noise, it is impossible to directly measure the braking index n of a magnetar. Based on the estimated ages of their potentially associated supernova remnants (SNRs), we estimate the values of the mean braking indices of eight magnetars with SNRs, and find that they cluster in the range of 1–42. Five magnetars have smaller mean braking indices of 1 〈  n  〈 3, and we interpret them within a combination of magneto-dipole radiation and wind-aided braking. The larger mean braking indices of n  〉 3 for the other three magnetars are attributed to the decay of external braking torque, which might be caused by magnetic field decay. We estimate the possible wind luminosities for the magnetars with 1 〈  n  〈 3, and the dipolar magnetic field decay rates for the magnetars with n  〉 3, within the updated magneto-thermal evolution models. Although the constrained range of the magnetars’ braking indices is tentative, as a result of the uncertainties in the SNR ages due to distance uncertainties and the unknown conditions of the expanding shells, our method provides an effective way to constrain the magnetars’ braking indices if the measurements of the SNR ages are reliable, which can be improved by future observations.
Print ISSN: 0035-8711
Electronic ISSN: 1365-2966
Topics: Physics
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• 3
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Oxford University Press
Publication Date: 2014-07-27
Print ISSN: 0035-8711
Electronic ISSN: 1365-2966
Topics: Physics
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• 4
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Oxford University Press
Publication Date: 2014-06-19
Description: In this work, we try to use the apparent luminosity versus displacement (i.e. L X versus R ) correlation of high-mass X-ray binaries (HMXBs) to constrain the common envelope (CE) efficiency α CE , which is a key parameter affecting the evolution of the binary orbit during the CE phase. The major updates that are crucial for the CE evolution include a variable parameter and a new CE criterion for Hertzsprung gap donor stars, both of which are recently developed. We find that, within the framework of the standard energy formula for CE and core definition at mass X  = 10 per cent, a high value of α CE , i.e. around 0.8–1.0, is more preferable, while α CE  〈 ~0.4 likely can not reconstruct the observed L X versus R distribution. However, due to an ambiguous definition for the core boundary in the literature, the used here still carries almost two order of magnitude uncertainty, which may translate directly to the expected value of α CE . We present the detailed components of current HMXBs and their spatial offsets from star clusters, which may be further testified by future observations of HMXB populations in nearby star-forming galaxies.
Print ISSN: 0035-8711
Electronic ISSN: 1365-2966
Topics: Physics
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• 5
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Oxford University Press
Publication Date: 2013-12-18
Description: Using an updated population synthesis code initially developed by Hurley et al., we modelled the synthetic X-ray binary (XRB) populations for direct comparison with the universal, featureless X-ray luminosity function (XLF) of high-mass X-ray binaries (HMXBs) in star-forming galaxies. Our main goal is to use the universal XLF to constrain the model parameters, given the current knowledge of binary evolution. We find that the one-dimensional (1D) Maxwellian velocity dispersion of the natal kick can be constrained to be of the order of kick  ~ 150 km s –1 , supporting earlier findings that neutron stars formed in binaries seem to receive significantly smaller natal kicks than the velocities of Galactic single pulsars would indicate. The super-Eddington accretion factor is further confirmed in the framework of stellar mass black holes (BHs), revealing that the true origin of most of the ultraluminous X-ray sources (ULXs) may indeed be the high-luminosity extension of ordinary HMXBs which harbour stellar mass BHs rather than exotic intermediate-mass BHs or ones. We present the detail properties of the model-predicted present-day HMXBs, which may be investigated by future high-resolution X-ray and optical observations of sources in nearby star-forming galaxies.
Print ISSN: 0035-8711
Electronic ISSN: 1365-2966
Topics: Physics
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• 6
Publication Date: 2016-12-13
Description: We present a timing analysis of two Rossi X-ray Timing Explorer observations of the microquasar GRS 1915+105 during the heartbeat state. The phase–frequency–power maps show that the intermediate-frequency aperiodic X-ray variability weakens as the source softens in the slow rise phase, and when the quasi-periodic oscillation disappears in the rise phase of the pulse of the double-peaked class, its sub-harmonic is still present with a hard phase lag. In the slow rise phase, the energy–frequency–power maps show that most of the aperiodic variability is produced in the corona, and may also induce the aperiodic variability observed at low energies from an accretion disc, which is further supported by the soft phase lag especially in the intermediate-frequency range (with a time delay up to 20 ms). In the rise phase of the pulse, the low-frequency aperiodic variability is enhanced significantly and there is a prominent hard lag (with a time delay up to 50 ms), indicating that the variability is induced by extension of the disc towards small radii as implied by the increase in flux and propagates into the corona. However, during the hard pulse of the double-peaked class, the variability shows no significant lag, which may be attributed to an optically thick corona. These timing results are generally consistent with the spectral results presented by Neilsen, Remillard & Lee which indicated that the slow rise phase corresponds to a local Eddington limit and the rise phase of the pulse corresponds to a radiation pressure instability in the disc.
Print ISSN: 0035-8711
Electronic ISSN: 1365-2966
Topics: Physics
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• 7
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Oxford University Press
Publication Date: 2011-10-14
Description: SUMMARY In this paper, we conduct ambient noise seismic tomography of northwestern China and adjacent regions. The data include 9 months (2009 January to 2009 September) three-component continuous data recorded at 146 seismic stations of newly upgraded China Provincial Digital Seismic Networks and regional Kyrgyzstan and Kazakhstan networks. Empirical Rayleigh and Love wave Green's functions are obtained from interstation cross-correlations. Group velocity dispersion curves for both Rayleigh and Love waves between 7 and 50 s periods were measured for each interstation path by applying the multiple-filter analysis method with phase-matched processing. The group velocity maps show clear lateral variations which correlate well with major geological structures and tectonic units in the study region. Shear wave velocity structures are inverted from Rayleigh wave and love wave dispersion maps. The results show that the Tibetan Plateau has a very thick crust with a low-velocity zone in its mid-lower crust. Along the northern margin of the plateau where a steep topographic gradient is present, the low-velocity zone does not extend to the Tarim basin which may indicate that crustal materials beneath the Tarim basin are colder and stronger than beneath the plateau, therefore inhibit the extension of mid-lower crustal flow and deformation of the Tibetan Plateau, resulting in very sharp topography contrasts. In the northeastern margin with a gentle topographic gradient toward the Ordos platform, the low-velocity zone diminishes around the eastern KunLun fault. Meanwhile, our results reveal obvious lateral velocity changes in the crust beneath the Tarim basin. In the upper crust, the Manjaer depression in the eastern Tarim basin is featured with very low velocities and the Bachu uplift in the western Tarim basin with high velocities; in the mid-lower crust, the northern Tarim basin in general displays lower velocities than the southern part along latitude ∼40° N with an east–west striking, which is consistent with the high magnetic anomaly zone and may be related to the central suture belt connecting the south and north of Tarim basement blocks together in Pre-Sinian.
Print ISSN: 0956-540X
Electronic ISSN: 1365-246X
Topics: Geosciences
Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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• 8
Unknown
Oxford University Press
Publication Date: 2013-05-08
Description: There are three categories of stars whose masses have been found accurately in recent times: (1) two for which Shapiro delay is used, which is possible due to GR light bending as the partner is heavy – PSR J1614–2230 and PSR J1903+0327, (2) six eclipsing stars for which numerical Roche lobe geometry is used and (3) three stars for which spectroscopic methods are used and in fact for these three the mass and radii both are estimated. Motivated by large colour ( N c ) expansion using a modified Richardson potential, along with density-dependent quark masses thereby allowing chiral symmetry restoration, we get compact strange stars fitting all the observed masses.
Print ISSN: 0035-8711
Electronic ISSN: 1365-2966
Topics: Physics
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• 9
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Oxford University Press
Publication Date: 2015-04-23
Description: We propose a method using the redshift dependence of the Alcock–Paczynski (AP) test and volume effect to measure the cosmic expansion history. The galaxy two-point correlation function as a function of angle, (μ), is measured at different redshifts. Assuming an incorrect cosmological model to convert galaxy redshifts to distances, the shape of (μ) appears anisotropic due to the AP effect, and the amplitude is shifted by the change in comoving volume. Due to the redshift dependence of the AP and volume effect, both the shape and amplitude of (μ) exhibit redshift dependence. Similar to Li et al. ( 2014 ), we find that the redshift-space distortions (RSD) caused by galaxy peculiar velocities, although significantly distorting (μ), exhibit much less redshift evolution compared to the AP and volume effects. By focusing on the redshift dependence of (μ), we can correctly recover the cosmological parameters despite the contamination of RSD. The method is tested by using the Horizon Run 3 N -body simulation, from which we made a series of 1/8-sky mock surveys having eight million physically self-bound haloes and sampled to have roughly a uniform number density in z  = 0–1.5. We find the AP effect results in tight, unbiased constraints on the density parameter and dark energy equation of state, with 68.3% CL intervals m  ~ 0.03 and w  ~ 0.1, and the volume effect leads to much tighter constraints of m  ~ 0.007 and w  ~ 0.035.
Print ISSN: 0035-8711
Electronic ISSN: 1365-2966
Topics: Physics
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• 10
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Oxford University Press
Publication Date: 2016-02-28
Description: We use the evolutionary population synthesis method to investigate the statistical properties of the wind-fed neutron-star (NS) compact ( P orb 〈 10 d) high-mass X-ray binaries (HMXBs) in our Galaxy, based on different spin-down models. Model 1 assumes that the surrounding material is treated as forming a quasi-static atmosphere. Model 2 assumes that the characteristic velocity of matter and the typical Alfvén velocity of material in the magnetospheric boundary layer are comparable to the sound speed in the external medium. We find that the spin-down rate in the supersonic propeller phase in either model 1 or model 2 is too low to produce the observed number of compact HMXBs. Model 3 assumes that the infalling material is ejected with the corotation velocity at the magnetospheric radius when the magnetospheric radius is larger than the corotation radius. Model 4 uses simple integration of the magnetic torque over the magnetosphere. Both models 3 and 4 have a larger spin down rate than that given by model 1 or 2. We also find that models 3 and 4 can predict a reasonable number of observed wind-fed NS compact HMXBs. By comparing our calculated results with the observed particular distributions of wind-fed NS compact HMXBs in a P s versus P orb diagram, we find that the subsonic propeller phase may not exist at all. However, the spin-down rates in models 3 and 4 both seem reasonable to produce the observed distribution of wind-fed NS compact HMXBs in the P s versus P orb diagram. We cannot find which spin-down rate seems more reasonable from our calculations.
Print ISSN: 0035-8711
Electronic ISSN: 1365-2966
Topics: Physics
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